For fractionating and purifying synthesis gases, it is known to use production plants in which one generally can only separate one part of the synthesis gas that has been produced by the partial oxidation of natural gas. In these known methods, carbon monoxide is separated by means of refrigeration engineering in one plant, which is known as a device for partial gas condensation (1). Means of refrigeration engineering are also employed to obtain the synthesis gas required for ammonia production, where a plant uses a method that is known as “nitrogen washing” (1). Both plants have a completely different construction type. The only common feature of these two techniques of refrigeration engineering is to be found in the use of a multiway plate heat exchanger for cooling off and reheating the gas streams. Each of these methods requires a cooling device, which in a partial condensation unit in general can utilizes the expansion of carbon monoxide or hydrogen, in which case a unit for nitrogen washing requires liquid nitrogen.